Positive electrode active material for lithium secondary battery and secondary battery comprising same

Abstract

A positive electrode active material for a lithium secondary battery according to an embodiment of the present disclosure may include: first positive electrode active material particles including a lithium metal oxide containing nickel, cobalt, and manganese; and second positive electrode active material particles including a lithium phosphate compound, in the first positive electrode active material particles, the molar ratio of cobalt in the total number of moles of nickel, cobalt, and manganese is greater than 0 and less than 0.15, and the weight ratio of the first positive electrode active material particles and the second positive electrode active material particles is 20: 80 to 80: 20. As a result, it is possible to achieve a lithium secondary battery having improved stability, capacity characteristics, and lifespan characteristics while saving production costs.

Description

Technical Field

[0001] The disclosure of the present application relates to a positive electrode active material for a lithium secondary battery and a secondary battery including the same. More specifically, it relates to a positive electrode active material for a lithium secondary battery including a plurality of lithium-based active materials and a lithium secondary battery including the same. Background Art

[0002] As a battery that can be repeatedly charged and discharged, a secondary battery is widely used as a power source for portable electronic devices such as mobile phones and laptop computers. A lithium secondary battery has a high working voltage and energy density per unit weight, which is beneficial to the charging speed and weight reduction, and thus is being actively developed and applied.

[0003] A lithium secondary battery stores electrical energy through the difference in chemical potential when lithium ions are intercalated and deintercalated between the positive electrode and the negative electrode. Thus, as the positive electrode active material and the negative electrode active material of a lithium secondary battery, substances that allow reversible intercalation and deintercalation of lithium ions can be used.

[0004] For example, as the positive electrode active material, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), lithium manganese iron phosphate (LMFP), lithium iron phosphate (LFP), lithium nickel-cobalt-manganese oxide (NCM), lithium nickel-aluminum-manganese oxide (NCA), etc. are used.

[0005] Among the positive electrode active materials, the chemical stability of NCM-based active materials is deteriorated, LFP-based active materials have relatively low ionic conductivity, and it may not be possible to provide sufficient high-power characteristics. Summary of the Invention

[0006] One problem of the present disclosure is to provide a positive electrode active material for a lithium secondary battery that provides improved chemical stability and power.

[0007] One problem of the present disclosure is to provide a lithium secondary battery having improved chemical stability and power.

[0008] The positive electrode active material for a lithium secondary battery according to an exemplary embodiment may include: first positive electrode active material particles including a lithium metal oxide containing nickel, cobalt, and manganese; and second positive electrode active material particles including a lithium phosphate compound. In the first positive electrode active material particles, the molar ratio of cobalt in the total molar number of nickel, cobalt, and manganese is greater than 0 and less than 0.15, and the weight ratio of the first positive electrode active material particles to the second positive electrode active material particles is 20:80 to 80:20.

[0009] In some embodiments, it may be that in the first positive electrode active material particles, the molar ratio of cobalt in the total molar amount of nickel, cobalt, and manganese is from 0.01 to 0.10.

[0010] In some embodiments, it may be that the weight ratio of the first positive electrode active material particles to the second positive electrode active material particles is from 25:75 to 75:25.

[0011] In some embodiments, it may be that the weight ratio of the first positive electrode active material particles to the second positive electrode active material particles is from 30:70 to 70:30.

[0012] In some embodiments, it may be that the first positive electrode active material particles include a lithium metal oxide having a structure represented by the following Chemical Formula 1:

Chemical Formula 1

[0013] In some embodiments, it may be that in Chemical Formula 1, 0.01 ≤ y ≤ 0.10.

[0014] In some embodiments, it may be that the lithium phosphate compound includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0015] In some embodiments, it may be that the lithium iron phosphate has a structure represented by the following Chemical Formula 2:

Chemical Formula 2

[0016] In some embodiments, it may be that the lithium manganese iron phosphate has a structure represented by the following Chemical Formula 3:

Chemical Formula 3

[0017] It may be that a lithium secondary battery according to an exemplary embodiment includes: a positive electrode including a positive electrode active material layer containing the positive electrode active material for a lithium secondary battery as described above; and a negative electrode opposite to the positive electrode.

[0018] In some embodiments, it may be that the negative electrode includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material includes a carbon-based active material.

[0019] In some embodiments, it may be that the carbon-based active material includes artificial graphite.

[0020] In some embodiments, it may be that the carbon-based active material further includes natural graphite.

[0021] In some embodiments, it may be that the weight ratio of artificial graphite to natural graphite is from 99:1 to 5:5.

[0022] In some embodiments, it may be that the weight ratio of artificial graphite to natural graphite is from 8:2 to 6:4.

[0023] The positive electrode active material for a lithium secondary battery according to an embodiment of the present disclosure may contain first positive electrode active material particles including a lithium metal oxide and second positive electrode active material particles including a lithium phosphate compound at a specific mixing ratio. The lithium metal oxide contains cobalt at a predetermined molar ratio in the total molar number of nickel, cobalt, and manganese.

[0024] For example, it may be that high capacity and high power characteristics of a lithium secondary battery are ensured by the first positive electrode active material particles, and stability of the lithium secondary battery is ensured by the second positive electrode active material particles.

[0025] Accordingly, a lithium secondary battery manufactured using the positive electrode active material can improve chemical stability while improving capacity characteristics and life characteristics, and can produce a lithium secondary battery at a lower cost.

[0026] The positive electrode using the positive electrode active material and / or the lithium secondary battery including the same can be widely applied in green technology fields such as electric vehicles, battery charging stations, solar power generation using batteries, and wind power generation. In addition, the lithium secondary battery can be applied in eco-friendly electric vehicles, hybrid vehicles, etc. that are used to suppress air pollution and greenhouse gas emissions to prevent climate change. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 and Figure 2 are a schematic top view and a cross-sectional view showing a lithium secondary battery according to an exemplary embodiment, respectively. DETAILED DESCRIPTION

[0028] According to an embodiment of the present disclosure, there is provided a positive electrode active material that contains first positive electrode active material particles including a lithium metal oxide and second positive electrode active material particles including a lithium phosphate compound in a specific mixing ratio, and the lithium metal oxide contains cobalt in a predetermined molar ratio in the total molar number of nickel, cobalt, and manganese.

[0029] The lithium secondary battery according to an exemplary embodiment may include a positive electrode manufactured from the positive electrode active material.

[0030] The meanings of the terms "first" and "second" used in this specification do not limit the number or order of the objects modified by "first" and "second", but are only used to distinguish the different modified objects from each other.

[0031] Hereinafter, embodiments of the present disclosure will be described in further detail with reference to specific implementation examples and the drawings. However, this is only an example, and the present disclosure is not limited to the specific embodiments described exemplarily.

[0032] <Positive Electrode Active Material for Lithium Secondary Battery> The positive electrode active material for a lithium secondary battery according to an exemplary embodiment may include: first positive electrode active material particles including a lithium metal oxide containing nickel, cobalt, and manganese; and second positive electrode active material particles including a lithium phosphate compound.

[0033] In some embodiments, the positive electrode active material may substantially consist of first positive electrode active material particles and second positive electrode active material particles.

[0034] In some embodiments, the first positive electrode active material particles may include a lithium metal oxide having a structure represented by the following Chemical Formula 1:

Chemical Formula 1

[0035] The bonding relationship included in the layered structure or crystal structure of the positive electrode active material is represented by Chemical Formula 1, and other additional elements are not excluded. For example, Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Chemical Formula 1 is provided to represent the bonding relationship of these main active elements and should be understood to include the introduction and substitution of additional elements.

[0036] In one embodiment, on the basis of the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure may further be included. The auxiliary element may be mixed together into the layered structure / crystal structure to form a bond, and this situation should be understood to be included within the scope of the chemical structure represented by Chemical Formula 1.

[0037] The auxiliary element may include, for example, at least one selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Al, Mo, Ga, W, Y, La, Ta, and B. The auxiliary element may also be, for example, an auxiliary active element that contributes to the capacity / power activity of the positive electrode active material together with Co or Mn.

[0038] The positive electrode active material may further include a coating element or a doping element. For example, an element that is substantially the same as or similar to the above-mentioned auxiliary element may be used as the coating element or the doping element. For example, one or more of the above elements may be used alone or in combination to serve as the coating element or the doping element.

[0039] The coating element or the doping element is present on the surface of the first positive electrode active material particle, or may also penetrate through the surface of the first positive electrode active material particle and thus be included in the bonding structure represented by Chemical Formula 1.

[0040] For example, nickel (Ni) can be provided as a metal related to the capacity of a lithium secondary battery. The higher the content of nickel, the higher the capacity and power of the lithium secondary battery can be improved. However, when the content of nickel increases excessively, the lifespan is reduced, and it may be disadvantageous in terms of mechanical stability and electrical stability.

[0041] For example, cobalt (Co) can be a metal related to the conductivity or resistance of a lithium secondary battery. Although cobalt can improve the crystallinity and structural stability of the positive electrode active material, the supply and demand are unstable, and the price may be high.

[0042] For example, manganese (Mn) can be provided as a metal related to the mechanical stability and electrical stability of a lithium secondary battery.

[0043] In some embodiments, in the first positive electrode active material particles, the molar ratio of cobalt in the total molar number of nickel, cobalt, and manganese can be greater than 0 and less than 0.15. For example, when the molar ratio of cobalt is 0.15 or more, the battery production cost may be too high.

[0044] For example, the molar ratio of cobalt can be greater than 0 to 0.10, greater than 0 to 0.05, greater than 0 to 0.03, greater than 0 to 0.02, greater than 0 to 0.01, 0.001 to 0.10, 0.001 to 0.05, 0.001 to 0.03, 0.001 to 0.02, 0.001 to 0.01, 0.01 to 0.15, 0.01 to 0.10, 0.01 to 0.05, 0.01 to 0.03, or 0.01 to 0.02.

[0045] For example, in Chemical Formula 1, it can be 0 < y < 0.15, 0 < y ≤ 0.10, 0 < y ≤ 0.05, 0 < y ≤ 0.03, 0 < y ≤ 0.02, 0 < y ≤ 0.01, 0.001 ≤ y ≤ 0.10, 0.001 ≤ y ≤ 0.05, 0.001 ≤ y ≤ 0.03, 0.001 ≤ y ≤ 0.02, 0.001 ≤ y ≤ 0.01, 0.01 ≤ y ≤ 0.15, 0.01 ≤ y ≤ 0.10, 0.01 ≤ y ≤ 0.05, 0.01 ≤ y ≤ 0.03, or 0.01 ≤ y ≤ 0.02.

[0046] Within the above range, even if the molar ratio of cobalt, which is expensive, is small, the capacity, power, lifespan, and stability of the lithium secondary battery can be improved.

[0047] In one embodiment, in the first positive electrode active material particles, the molar ratio of cobalt in the total molar number of nickel, cobalt, and manganese can be greater than 0. For example, when the molar ratio of cobalt is 0, the crystallinity and structural stability of the positive electrode active material may deteriorate.

[0048] For example, the first positive electrode active material particles including a lithium metal oxide having a structure represented by Chemical Formula 1 may have improved lithium ion conductivity and power characteristics compared to the second positive electrode active material particles.

[0049] In one embodiment, the first positive electrode active material particles may be composed of a lithium metal oxide having a structure represented by Chemical Formula 1.

[0050] In some embodiments, the lithium phosphate compound may include at least one selected from the group consisting of lithium iron phosphate and lithium manganese iron phosphate. For example, the lithium phosphate compound may include lithium iron phosphate or lithium manganese iron phosphate.

[0051] In one embodiment, lithium iron phosphate contains iron (Fe) and phosphorus (P) and may not contain manganese (Mn).

[0052] In some embodiments, lithium iron phosphate may have a structure represented by the following Chemical Formula 2:

Chemical Formula 2

[0053] In some embodiments, lithium manganese iron phosphate may have a structure represented by the following Chemical Formula 3:

Chemical Formula 3

[0054] For example, the second positive electrode active material particles including at least one of lithium iron phosphate having a structure represented by Chemical Formula 2 and lithium manganese iron phosphate having a structure represented by Chemical Formula 3 may have improved crystal structure and chemical stability compared to the first positive electrode active material particles.

[0055] In one embodiment, the second positive electrode active material particles may be composed of lithium iron phosphate having a structure represented by Chemical Formula 2, or may be composed of lithium manganese iron phosphate having a structure represented by Chemical Formula 3.

[0056] In some embodiments, the first positive electrode active material particles and the second positive electrode active material particles may be contained in a weight ratio of 20:80 to 80:20. For example, the weight ratio may be 20:80 to 60:40, 20:80 to 50:50, 20:80 to 40:60, 20:80 to 35:65, 25:75 to 75:25, 25:75 to 60:40, 30:70 to 70:30, 30:70 to 60:40, or 30:70 to 40:60.

[0057] In the sum of the first positive electrode active material particles and the second positive electrode active material particles, when the content of the first positive electrode active material particles is less than 20% by weight, the power characteristics and capacity characteristics of the lithium secondary battery may deteriorate. When the content of the first positive electrode active material particles is higher than 80% by weight, the stability of the positive electrode active material may deteriorate.

[0058] In some embodiments, the positive electrode active material includes the first positive electrode active material particles and the second positive electrode active material particles together, so that even if the content of expensive cobalt is small, the capacity, power, life, and stability of the lithium secondary battery can be improved.

[0059] For example, even when the positive electrode active material contains a small amount of cobalt, the high capacity and high power characteristics of the lithium secondary battery can be ensured by the first positive electrode active material particles, and the stability of the lithium secondary battery can be ensured by the second positive electrode active material particles.

[0060] In some embodiments, the first positive electrode active material particles and the second positive electrode active material particles may have a secondary particle structure assembled from primary particles. For example, it may have the form of secondary particles aggregated from a plurality of primary particles.

[0061] <Lithium secondary battery> Figure 1 and Figure 2 are a schematic top view and a cross-sectional view showing a lithium secondary battery according to an exemplary embodiment, respectively. Figure 2 is a cross-sectional view taken along the line I-I' marked in Figure 1 in the thickness direction.

[0062] Referring to Figure 1 and Figure 2 , the lithium secondary battery may include: a positive electrode 100 including a positive electrode active material layer containing the above-described positive electrode active material for a lithium secondary battery; and a negative electrode 130 opposite to the positive electrode.

[0063] The positive electrode 100 may include a positive electrode active material layer 110 formed by coating the above-described positive electrode active material on a positive electrode current collector 105.

[0064] For example, the positive electrode active material according to the above embodiment may be mixed and stirred in a solvent with a binder, a conductive material, and / or a dispersing material, etc. to manufacture a slurry. The slurry may be coated on the positive electrode current collector 105, and then dried and compressed to manufacture the positive electrode 100.

[0065] Non-limiting examples of the solvent may include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0066] The coating process may be carried out by methods such as gravure coating, slot die coating, multi-layer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto.

[0067] The positive electrode current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or their alloys. The positive electrode current collector may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver. The positive electrode current collector is not limited thereto, and for example, it may be 10 μm to 50 μm.

[0068] The binder may include, for example, organic binders such as vinylidene fluoride-co-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or water-based binders such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0069] For example, as the binder for forming the positive electrode, a PVDF series binder may be used. In this case, the amount of the binder used for forming the positive electrode active material layer 110 can be reduced, and the amount of the positive electrode active material can be relatively increased, thereby improving the power and capacity of the secondary battery.

[0070] It may include a conductive material to facilitate electron movement between the active material particles. For example, the conductive material may include carbon series conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fiber, etc. and / or metal series conductive materials such as perovskite substances such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3.

[0071] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed by coating the negative electrode active material on the negative electrode current collector 125.

[0072] As the negative electrode active material, substances known in the art that can intercalate and deintercalate lithium ions can be used without limitation. For example, carbon series materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fiber, etc.; lithium metal; lithium alloy; silicon (Si)-containing substances or tin (Sn)-containing substances, etc. can be used as the negative electrode active material.

[0073] As an example of amorphous carbon, hard carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc. can be cited.

[0074] As an example of crystalline carbon, graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. can be cited.

[0075] Lithium metal can be pure lithium metal or lithium metal formed with a protective layer for suppressing dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on the negative electrode current collector can be used as the negative electrode active material layer. In one embodiment, it can also be a lithium thin film layer used as the negative electrode active material layer.

[0076] As elements included in the lithium alloy, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, etc. can be cited.

[0077] Silicon-containing substances can provide further increased capacity characteristics. The silicon-containing substances can include Si, SiO x (0 < x < 2), silicon-carbon composites, metal-doped silicates, or SiO x (0 < x < 2), etc. The metal can include lithium and / or magnesium.

[0078] In some embodiments, the negative electrode active material may include carbon-based active materials.

[0079] In some embodiments, the carbonaceous active material may include artificial graphite. For example, the carbonaceous active material may further include natural graphite. The mechanical stability of the battery can be improved by artificial graphite, and the capacity and power of the battery can be improved by natural graphite.

[0080] In some embodiments, the weight ratio of artificial graphite to natural graphite may be from 99:1 to 5:5, for example, from 8:2 to 6:4. Within this range, the mechanical stability, life characteristics, capacity characteristics, and power characteristics of the battery can be improved.

[0081] For example, it can be mixed and stirred with the above-mentioned binder, conductive material, and thickener in the negative electrode active material and the solvent to form a slurry. The slurry can be coated on at least one surface of the negative electrode current collector 125, and then compressed and dried to manufacture the negative electrode 130.

[0082] Non-limiting examples of the solvent may include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, etc.

[0083] The coating process may be carried out by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto.

[0084] As the binder and conductive material, substances substantially the same or similar to those used in the positive electrode active material layer 110 can be used. In some embodiments, for the compatibility with the carbon-based active material, the binder used to form the negative electrode may include, for example, water-based binders such as styrene-butadiene rubber (SBR), and can be used together with thickeners such as carboxymethyl cellulose (CMC).

[0085] In one embodiment, the separator 140 may be interposed between the positive electrode 100 and the negative electrode 130. The separator can prevent electrical short circuit between the positive electrode and the negative electrode and maintain the flow of ions. According to an embodiment, the thickness of the separator may be from 10 μm to 20 μm, but the present disclosure is not limited thereto.

[0086] The separator 140 may include a porous polymer membrane or a porous non-woven fabric. The porous polymer membrane may include polyolefin polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. The porous non-woven fabric may include high melting point glass fibers, polyethylene terephthalate fibers, etc.

[0087] The separator may also include ceramic materials. For example, inorganic particles may be coated on or dispersed in the polymer membrane to improve heat resistance.

[0088] The separator may have a single-layer or multi-layer structure including the above-mentioned polymer membrane and / or non-woven fabric.

[0089] In some embodiments, the area (e.g., the contact area with the separator 140) and / or volume of the negative electrode 130 may be larger than that of the positive electrode 100. Thus, lithium ions generated from the positive electrode 100 can move smoothly to the negative electrode 130 without precipitation in the middle, for example.

[0090] According to an exemplary embodiment, the positive electrode 100, the negative electrode 130, and the separator 140 may be repeatedly arranged to form the electrode assembly 150. In some embodiments, the electrode assembly 150 may have a jelly roll form formed by winding, stacking, z-folding, or stack-folding of the separator 140.

[0091] In one embodiment, the electrode assembly 150 may have a jelly roll form in which the positive electrode 100, the negative electrode 130, and the separator 140 are wound together. In one embodiment, the electrode assembly 150 may have a jelly roll form in which the positive and negative electrodes are arranged with cuts in the space formed by repeatedly z-folding the separator 140.

[0092] In one embodiment, the electrode assembly may be formed by repeatedly stacking the positive electrode, the negative electrode, and the separator with each layer being cut or separated from each other.

[0093] The electrode assembly 150 may be accommodated in the housing 160 together with the electrolyte to define a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte may be used as the electrolyte.

[0094] The non-aqueous electrolyte includes a lithium salt and an organic solvent as the electrolyte. The lithium salt is, for example, composed of Li + X -represents and, as the anion (X of the lithium salt - ), examples can be F - 、Cl - 、Br - 、I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - 、PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - 、CF3SO3 - 、CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - 、CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - 、CF3(CF2)7SO3 - 、CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - etc.

[0095] The organic solvent can include an organic compound that has sufficient solubility for the lithium salt and the additive and is non-reactive within the battery. As the organic solvent, it can include at least one of, for example, carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, and aprotic solvents.

[0096] As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, propylene sulfite, etc. can be used. They can be used alone or in combination of two or more kinds.

[0097] The non-aqueous electrolyte may further include an additive. The additive may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, etc.

[0098] The cyclic carbonate compounds may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0099] The fluorine-substituted carbonate compounds may include fluoroethylene carbonate (FEC), etc. Sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0100] Cyclic sulfate compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0101] Cyclic sulfite compounds may include ethylene sulfite, butylene sulfite, etc.

[0102] Phosphate compounds may include lithium difluoro bis-oxalatophosphate, lithium difluoro phosphate, etc.

[0103] Borate compounds may include lithium bis(oxalate)borate, etc.

[0104] As Figure 1 shown, each electrode tab (the positive electrode tab and the negative electrode tab) may respectively protrude from the positive electrode current collector 105 and the negative electrode current collector 125 belonging to each electrode monomer and extend to one side of the housing 160. The electrode tab may be fused together with one side of the housing 160 so as to be connected to the electrode leads (the positive electrode lead 107 and the negative electrode lead 127) extending or exposed to the outside of the housing 160.

[0105] The lithium secondary battery may be made into, for example, a cylindrical type using a can, a square type, a pouch type, a coin type, etc.

[0106] Hereinafter, with reference to specific experimental examples, the embodiments of the present invention will be further described. The embodiments and comparative examples included in the experimental examples are only used to exemplify the present disclosure and are not used to limit the scope of the appended patent claims. Those skilled in the art should clearly understand that various deformations and modifications can be made to the embodiments within the scope and technical concept of the present disclosure, and such deformations and modifications belong to the scope of the appended patent claims.

[0107] <Examples and Comparative Examples> (1)Manufacture of the positive electrode active material As described in Table 1 below, the first positive electrode active material particles and the second positive electrode active material particles were mixed to produce the positive electrode active materials of the examples and comparative examples.

[0108]

Table 1

[0109] (2)Manufacture of the lithium secondary battery The positive electrode active material produced in (1), carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 92:5:3 to produce a positive electrode paste.

[0110] The positive electrode paste was uniformly coated on the area of an aluminum foil (15 μm thick) having a protrusion (positive electrode tab) on one side except for the protrusion, dried, and then calendered to produce a positive electrode.

[0111] A mixture of artificial graphite and natural graphite (weight ratio of 7:3) as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a thickener were mixed at a weight ratio of 97:1:2 to produce a negative electrode paste.

[0112] The negative electrode paste was uniformly coated on the area of an aluminum foil (15 μm thick) having a protrusion (negative electrode tab) on one side except for the protrusion, dried, and then calendered to produce a negative electrode.

[0113] A polyethylene separator (20 μm thick) was interposed between the positive electrode and the negative electrode to form an electrode assembly. Then, a positive electrode lead and a negative electrode lead were welded to the positive electrode tab and the negative electrode tab, respectively, for connection.

[0114] The electrode assembly was housed inside a soft package (case), and three sides except for the electrolyte injection part surface were sealed to expose partial areas of the positive electrode lead and the negative electrode lead to the outside.

[0115] An electrolytic solution was injected, the electrolyte injection part surface was also sealed, and then it was impregnated for 12 hours to produce a secondary battery.

[0116] As the electrolyte, after manufacturing a 1M LiPF6 solution (a mixed solvent of EC / EMC / DEC with a volume ratio of 25:30:45), 1 wt% of FEC (fluoroethylenecarbonate), 0.3 wt% of VC (vinylethylene carbonate), 1.0 wt% of LiPO2F2 (lithium difluorophosphate), 0.5 wt% of PS (1,3-propanesultone), and 0.5 wt% of PRS (prop-1-ene-1,3-sultone) were added and mixed based on the total weight of the electrolyte.

[0117] <Experimental Examples> Experimental Example 1: Evaluation of the DSC heat generation amount For the lithium secondary batteries of the examples and comparative examples, the heat change was measured using a differential scanning calorimetry (DSC) device, and the method of heating from 25°C to 450°C at a rate of 5°C per minute was carried out.

[0118] The calorific value obtained by integrating the heat generation numerical curve on the DSC with respect to temperature is recorded in Table 2 below.

[0119] Experimental Example 2: Evaluation of the initial capacity After charging the lithium secondary batteries of the examples and comparative examples at 0.1C-rate CC / CV at 25°C (4.2V, 0.05C cut-off), they were discharged at 0.1C-rate CC (cut-off at 2.5V) 3 times.

[0120] The second discharge capacity value was taken as the initial capacity C1 of the lithium secondary battery and recorded in Table 2 below.

[0121] Experimental Example 3: Evaluation of the capacity retention rate after high-temperature storage The lithium secondary batteries of the examples and comparative examples were charged to 4.2V at 0.1C at 25°C and placed at a high temperature (60°C) for 4 weeks. After the high-temperature placement, the lithium secondary batteries were discharged at 0.1C-rate CC (cut-off at 2.5V) to measure the discharge capacity C2.

[0122] The capacity retention rate after high-temperature storage was calculated according to the following formula, and the results are recorded in Table 2 below.

[0123] Capacity retention rate (%) = (C2 / C1) × 100.

[0124] Experimental Example 4: Evaluation of the gas generation amount after high-temperature storage The lithium secondary batteries of the examples and comparative examples were charged at 0.1C to 4.2V at 25°C, placed at a high temperature (60°C) for 4 weeks, and then the gas generation amount was confirmed by gas chromatography (GC) analysis.

[0125] To measure the total gas generation amount, a hole was formed in a vacuum chamber of a predetermined volume V, the pressure change was measured, and thus the gas generation volume was calculated, and the results are shown in Table 2 below.

[0126]

Table 2

[0127] 1) : Storage at 60°C 2) : Storage at 60°C.

[0128] Referring to Table 1 and Table 2, in the lithium secondary batteries of the examples, while the DSC heat generation amount and the gas generation amount were reduced, the capacity characteristics and the life characteristics were improved.

[0129] In the lithium secondary batteries of Comparative Examples 1 and 4 that do not include the second positive electrode active material particles, the DSC heat generation amount and the gas generation amount are high, and in the lithium secondary battery of Comparative Example 2 that does not include the first positive electrode active material particles, the discharge capacity is low.

[0130] In the lithium secondary batteries of Comparative Examples 3, 5, and 6 that include the second positive electrode active material particles but have a cobalt molar ratio greater than 0.15 in the total molar number of nickel, cobalt, and manganese as the first positive electrode active material particles, the gas generation amount is high or the discharge capacity is low.

Claims

1. A positive electrode active material for a lithium secondary battery, comprising: First positive electrode active material particles including lithium metal oxide containing nickel, cobalt and manganese; and The second positive electrode active material particles include a lithium phosphate compound, In the first positive electrode active material particles, the molar ratio of cobalt in the total molar number of nickel, cobalt and manganese is greater than 0 and less than 0.15, A weight ratio of the first positive electrode active material particles to the second positive electrode active material particles is 20:80 to 80:

20.

2. The positive electrode active material for lithium secondary battery according to claim 1, wherein In the first positive electrode active material particles, a molar ratio of cobalt in the total moles of nickel, cobalt and manganese is 0.01 to 0.

10.

3. The positive electrode active material for lithium secondary battery according to claim 1, wherein A weight ratio of the first positive electrode active material particles to the second positive electrode active material particles is 25:75 to 75:

25.

4. The positive electrode active material for lithium secondary battery according to claim 3, wherein A weight ratio of the first positive electrode active material particles to the second positive electrode active material particles is 30:70 to 70:

30.

5. The positive electrode active material for lithium secondary battery according to claim 1, wherein The first positive electrode active material particles include a lithium metal oxide having a structure represented by the following Chemical Formula 1: 【Chemical formula 1】 Li b Ni x Co y Mr z M1 k O 2+a In Chemical Formula 1, M1 includes at least one selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Al, Mo, Ga, W, Y, La, Ta, and B, 0.5≤x≤1.0, 0 <y<0.15,0<z≤0.3,0≤k≤0.2,x+y+z+k=1,0≤a≤0.5,0.9≤b≤1.2。 6. The positive electrode active material for lithium secondary battery according to claim 5, wherein In Chemical Formula 1, 0.01≤y≤0.

10.

7. The positive electrode active material for lithium secondary battery according to claim 1, wherein The lithium phosphate compound includes at least one selected from the group consisting of lithium iron phosphate and lithium manganese iron phosphate.

8. The positive electrode active material for lithium secondary battery according to claim 7, wherein The lithium iron phosphate has a structure represented by the following Chemical Formula 2: 【Chemical formula 2】 <h2 style=";text-align:left;direction:ltr">Li<h2 style=";text-align:left;direction:ltr"> c <h2 style=";text-align:left;direction:ltr"> Fe<h2 style=";text-align:left;direction:ltr"> d <h2 style=";text-align:left;direction:ltr"> M2<h2 style=";text-align:left;direction:ltr"> e <h2 style=";text-align:left;direction:ltr"> PO4 In Chemical Formula 2, M2 is at least one selected from the group consisting of Ni, Co, Mg, Y, Zn, Ru, Ti, Nb, Mo, Cr, Cu, Zr, W, Ir and V, 0.9≤c≤1.5, 0.15≤d≤1, and 0≤e≤0.

9.

9. The positive electrode active material for lithium secondary battery according to claim 7, wherein The lithium manganese iron phosphate has a structure represented by the following Chemical Formula 3: 【Chemical formula 3】 <h2 style=";text-align:left;direction:ltr">Li<h2 style=";text-align:left;direction:ltr"> f <h2 style=";text-align:left;direction:ltr"> Fe<h2 style=";text-align:left;direction:ltr"> g <h2 style=";text-align:left;direction:ltr"> Mn<h2 style=";text-align:left;direction:ltr"> h <h2 style=";text-align:left;direction:ltr"> M3<h2 style=";text-align:left;direction:ltr"> i <h2 style=";text-align:left;direction:ltr"> PO4 In Chemical Formula 3, M3 is at least one selected from the group consisting of Ni, Co, Mg, Y, Zn, Ru, Ti, Nb, Mo, Cr, Cu, Zr, W, Ir and V, 0.9≤f≤1.5, 0.01≤g≤0.3, 0.6≤h≤0.99, and 0≤i≤0.

1.

10. A lithium secondary battery comprising: A positive electrode comprising a positive electrode active material layer containing the positive electrode active material for a lithium secondary battery according to claim 1; and A negative electrode is opposite to the positive electrode.

11. The lithium secondary battery according to claim 10, wherein: The negative electrode includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material includes a carbon-based active material.

12. The lithium secondary battery according to claim 11, wherein The carbon-based active material includes artificial graphite.

13. The lithium secondary battery according to claim 12, wherein: The carbon-based active material also includes natural graphite.

14. The lithium secondary battery according to claim 13, wherein: The weight ratio of artificial graphite to natural graphite is 99:1 to 5:

5.

15. The lithium secondary battery according to claim 14, wherein: The weight ratio of artificial graphite to natural graphite is 8:2 to 6:4.

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